Various manufacturing, agricultural, contamination remediation and industrial processes produce a waste gas stream having dilute hydrocarbon concentrations generally in air. Some applications include those where the VOC is entrained in a solid or liquid media such as contaminated soil or water. The VOC can be converted to gas and separated from the solid or liquid media. Other processes produce or contain gaseous VOC. A number of processes exist to burn or oxidize the VOC, but the present invention is directed to recovering energy. If the concentration of VOC is sufficiently great, and they are suitable to operate an engine, they may be directly supplied to an engine that produces rotary power or electricity. In other cases, these dilute hydrocarbon concentrations are sometimes insufficient in their energy content to efficiently operate an engine directly. Engines include devices that convert chemical energy into electrical or kinetic energy such as combustion engines (internal or external), Stirling cycle or turbine engines. In other situations, the waste gas stream has sufficient energy content to operate an engine, but the form of the hydrocarbon is such that the engine requires extensive modification to operate using the waste gas directly. For example, the waste gas may include complex hydrocarbons of varying concentrations or particulates. These gases may harm the ECD if they are not treated or converted to reformate.
Manufacturing processes that produce waste gas streams with a dilute hydrocarbon concentration are currently flared or burned or supplied to an engine as part of the combustion air. Flaring the waste gas does not return any energy. Burning the waste gas produces heat. Recovering electrical or kinetic energy is generally much more valuable than recovered heat energy. GB patent application 2364257, published Jan. 1, 2002, and incorporated herein by reference, splits a gas stream having VOC into two streams. The first stream is directed to the combustion air intake of an engine and the second stream is directed to a combustion unit. Exhaust heat from the engine mixes with and combusts the second stream. This reference does not teach concentrating the VOC nor directing the VOC to the fuel intake of the engine. WO9530470, published Nov. 16, 1995, and incorporated herein by reference, teaches a device to burn VOC in an engine by having two adsorption/desorption units so that the waste gas stream and engine may operate independently of one another. The first unit may collect and concentrate VOC as needed and the second unit supplies VOC to the engine as needed. This reference and the GB reference leave the VOC in the combustion air and do not feed the VOC to the fuel intake of the engine. US 2002/0100277 published Aug. 1, 2002, and incorporated herein by reference also teaches directing VOC to an internal combustion engine, but the device does not concentrate the VOC. Their concentration is based on the vapor pressure of the VOC in the container. VOC not directed to the engine are condensed into a liquid by a chiller, but these liquefied VOC are not supplied to the engine as a fuel.
It is known that waste gases can be directly supplied to the combustion or exhaust air of an engine. One commercially available device supplies waste gases from an industrial operation to a turbine engine. In a paper by Neill and Gunter, VOC Destruction using Combustion Turbines, published September 2002, and incorporated herein by reference, describes a device that combines waste VOC with natural gas to operate a gas turbine. The gas turbine produces electricity for the facility. The waste gases come directly from the exhaust air of the industrial operation and are supplied to the engine as part of the combustion air. The turbine engine has a separate fuel source to supply the majority of the fuel. The exhaust air provides a relatively low (200 to 5000 ppm of unburned hydrocarbons and VOC) percentage of the energy content needed to operate the engine. Devices like this require an external fuel supply as part of the normal operation of the device. The external fuel supply is not merely a part of start-up or load leveling operation. These references teach directly supplying VOC to the engine without filtering and require an engine capable of consuming these VOC. By directing the VOC to the combustion air, a very large engine/generator is needed. The example given in Neill and Gunter is a 20MW turbine to abate 150,000 Standard Cubic Feet per Minute (scfm) of air.
U.S. Pat. No. 5,451,249, issued Sep. 19, 1995, and incorporated herein by reference, teaches a device and method to supply a gas stream from a landfill to be used as the fuel source of a fuel cell. The natural gas component of the landfill gas is desirable and the VOC contained in the landfill gas is removed and are not used to supply fuel to the fuel cell. The 5,451,249 patent describes heavy hydrocarbons as contaminant fractions that must be removed from the gas stream prior to reforming. Rather than teaching that these VOC are a contaminant, the present invention utilizes these hydrocarbons as the fuel for an engine.
The present invention is directed to a device and method to utilize the energy from VOC by using the VOC as the primary fuel for an engine. The present invention is capable of producing high value kinetic or electrical energy from waste gases. The invention reclaims dilute VOC from a waste gas stream. The invention will be illustrated using exhaust air from an automotive paint booth, but many other manufacturing, chemical, industrial, agricultural, and waste management processes produce dilute VOC gas streams that would be suitable for this invention. The dilute VOC gas stream are organic compounds that evaporate readily into air and may contain straight chain, branched, aromatic, or oxygenated hydrocarbons. The invention has the dual advantage of abating the hydrocarbons while producing energy. The engine may be any variety of internal or external combustion engine, a Stirling cycle engine, a gas turbine or another engine that can produce kinetic energy usually in the form of output shaft power, or electricity. The invention is an energy efficient method to utilize the hydrocarbons entrained in the gas stream present in, or exhausted from, manufacturing, industrial, agricultural, environmental, chemical or waste processes.